bufsize: go gen and docs (#3449)

Run 'go generate' and 'make -f Makefile.doc' to generate the chaos
plugin author list and update the manual pages.

Signed-off-by: Miek Gieben <miek@miek.nl>

man/coredns-bufsize.7

@@ -0,0 +1,67 @@
+.\" Generated by Mmark Markdown Processer - mmark.miek.nl
+.TH "COREDNS-BUFSIZE" 7 "November 2019" "CoreDNS" "CoreDNS Plugins"
+
+.SH "NAME"
+.PP
+\fIbufsize\fP - sizes EDNS0 buffer size to prevent IP fragmentation.
+
+.SH "DESCRIPTION"
+.PP
+\fIbufsize\fP limits a requester's UDP payload size.
+It prevents IP fragmentation so that to deal with DNS vulnerability.
+
+.SH "SYNTAX"
+.PP
+.RS
+
+.nf
+bufsize [SIZE]
+
+.fi
+.RE
+
+.PP
+\fB[SIZE]\fP is an int value for setting the buffer size.
+The default value is 512, and the value must be within 512 - 4096.
+Only one argument is acceptable, and it covers both IPv4 and IPv6.
+
+.SH "EXAMPLES"
+.PP
+Enable limiting the buffer size of outgoing query to the resolver (172.31.0.10):
+
+.PP
+.RS
+
+.nf
+\&. {
+    bufsize 512
+    forward . 172.31.0.10
+    log
+}
+
+.fi
+.RE
+
+.PP
+Enable limiting the buffer size as an authoritative nameserver:
+
+.PP
+.RS
+
+.nf
+\&. {
+    bufsize 512
+    file db.example.org
+    log
+}
+
+.fi
+.RE
+
+.SH "CONSIDERATIONS"
+.IP \(bu 4
+Setting 1232 bytes to bufsize may avoid fragmentation on the majority of networks in use today, but it depends on the MTU of the physical network links.
+.IP \(bu 4
+For now, if a client does not use EDNS, this plugin adds OPT RR.
+
+